1. Field of the Invention
This invention relates to a method and an apparatus for generating a signal having a set of orthogonal multiple carriers modulated in accordance with information to be transmitted. Also, this invention relates to a method and apparatus for decoding or demodulating an orthogonal-multi-carrier signal into data or information.
2. Description of the Related Art
Orthogonal frequency division multiplexing (OFDM) employs multiple carriers which are orthogonal with respect to each other. The xe2x80x9corthogonalxe2x80x9d multiple carriers mean that the spectrums of carriers neighboring one carrier are null at the frequency of the latter carrier. The multiple carriers are modulated in accordance with digital information pieces to be transmitted, respectively. For example, phase modulation or quadrature amplitude modulation is used by the carrier modulation. The modulation-resultant multiple carriers are combined into an OFDM signal which has a form as a random signal.
Generally, an OFDM transmitter side uses inverse discrete Fourier transform (IDFT) in generating an OFDM signal, that is, an orthogonal-multi-carrier signal. Specifically, information pieces to be transmitted are subjected to IDFT in frequency domain, being converted into an OFDM signal in time domain. An OFDM receiver side demodulates a received OFDM signal into frequency-domain information pieces through discrete Fourier transform (DFT).
Regarding an OFDM transmission system, it is desirable to use some carriers (for example, alternate carriers) among a full set, that is, an unthinned set of orthogonal multiple carriers in a limited frequency band. Such a carrier thinning technique is advantageous in reducing a system cost and meeting a power reducing requirement.
A consideration will be given of the case where xe2x80x9cmxe2x80x9d carriers spaced at xe2x80x9cnxe2x80x9d-carrier intervals are used among an unthinned set, that is, a full set of xe2x80x9cnxc3x97mxe2x80x9d orthogonal multiple carriers where xe2x80x9cxc3x97xe2x80x9d denotes multiplication or product. Even in this case, an nxc3x97m-point IDFT circuit is employed which can generate xe2x80x9cnxc3x97mxe2x80x9d orthogonal multiple carriers. Here, xe2x80x9cnxc3x97mxe2x80x9d orthogonal multiple carriers are separated into xe2x80x9cmxe2x80x9d groups each having xe2x80x9cnxe2x80x9d neighboring carriers. The nxc3x97m-point IDFT circuit is operated so that one carrier of each of the xe2x80x9cmxe2x80x9d groups will be modulated in accordance with a corresponding effective information piece while (nxe2x88x921) remaining carriers in each group will be modulated in accordance with zero data pieces and thus be prevented from actually appearing. In other words, the (nxe2x88x921) remaining carriers in each group are set as carrier holes. The nxc3x97m-point IDFT circuit tends to be large in scale and high in cost.
Regarding OFDM transmission, it is known to assign some carriers among orthogonal multiple carriers to pilot signals other than main information pieces to be transmitted.
It is a first object of this invention to provide an inexpensive method of generating an orthogonal-multi-carrier signal.
It is a second object of this invention to provide an inexpensive apparatus for generating an orthogonal-multi-carrier signal.
It is a third object of this invention to provide an inexpensive method of decoding or demodulating an orthogonal-multi-carrier signal into data or information.
It is a fourth object of this invention to provide an inexpensive apparatus for decoding or demodulating an orthogonal-multi-carrier signal into data or information.
A first aspect of this invention provides a method comprising the steps of generating a first orthogonal-multi-carrier signal through N-point inverse discrete Fourier transform, the first orthogonal-multi-carrier signal having xe2x80x9cNxe2x80x9d or less orthogonal multiple carriers, where xe2x80x9cNxe2x80x9d denotes a predetermined natural number equal to or greater than 2; and repeating every 1-unit time segment of the first orthogonal-multi-carrier signal xe2x80x9cMxe2x80x9d times to generate every 1-symbol time segment of a second orthogonal-multi-carrier signal, the second orthogonal-multi-carrier signal having a thinned set of xe2x80x9cNxe2x80x9d or less orthogonal multiple carriers spaced at M-carrier intervals, where xe2x80x9cMxe2x80x9d denotes a predetermined natural number equal to or greater than 2.
A second aspect of this invention provides a method comprising the steps of dividing every 1-symbol time segment of a first orthogonal-multi-carrier signal into xe2x80x9cMxe2x80x9d successive 1/M-symbol time segments, the first orthogonal-multi-carrier signal having a thinned set of xe2x80x9cNxe2x80x9d or less orthogonal multiple carriers spaced at M-carrier intervals, where xe2x80x9cMxe2x80x9d denotes a predetermined natural number equal to or greater than 2, and xe2x80x9cNxe2x80x9d denotes a predetermined natural number equal to or greater than 2; adding and averaging at least two of the xe2x80x9cMxe2x80x9d successive 1/M-symbol time segments of the first orthogonal-multi-carrier signal into a 1-unit time segment of a second orthogonal-multi-carrier signal; and subjecting the second orthogonal-multi-carrier signal to N-point discrete Fourier transform for every unit time interval.
A third aspect of this invention provides a method comprising the steps of generating a first orthogonal-multi-carrier signal through N-point inverse discrete Fourier transform, the first orthogonal-multi-carrier signal having xe2x80x9cNxe2x80x9d or less orthogonal multiple carriers, where xe2x80x9cNxe2x80x9d denotes a predetermined natural number equal to or greater than 2; repeating every 1-unit time segment of the first orthogonal-multi-carrier signal xe2x80x9cMxe2x80x9d times to generate every 1-symbol time segment of a second orthogonal-multi-carrier signal, the second orthogonal-multi-carrier signal having a thinned set of xe2x80x9cNxe2x80x9d or less orthogonal multiple carriers spaced at M-carrier intervals, where xe2x80x9cMxe2x80x9d denotes a predetermined natural number equal to or greater than 2; generating a third orthogonal-multi-carrier signal through Mxc3x97N-point inverse discrete Fourier transform, the third orthogonal-multi-carrier signal having xe2x80x9cMxc3x97N-Lxe2x80x9d orthogonal multiple carriers, where xe2x80x9cLxe2x80x9d denotes a predetermined natural number equal to or greater than the number xe2x80x9cNxe2x80x9d; and combining the second orthogonal-multi-carrier signal and the third orthogonal-multi-carrier signal into a fourth orthogonal-multi-carrier signal.
A fourth aspect of this invention is based on the third aspect thereof, and provides a method further comprising the steps of dividing every 1-symbol time segment of the fourth orthogonal-multi-carrier signal into xe2x80x9cMxe2x80x9d successive 1/M-symbol time segments; adding and averaging at least two of the xe2x80x9cMxe2x80x9d successive 1/M-symbol time segments of the fourth orthogonal-multi-carrier signal into a 1-unit time segment of a fifth orthogonal-multi-carrier signal; and subjecting the fifth orthogonal-multi-carrier signal to N-point discrete Fourier transform for every unit time interval.
A fifth aspect of this invention is based on the third aspect thereof, and provides a method wherein the third orthogonal-multi-carrier signal contains a pilot signal.
A sixth aspect of this invention provides an apparatus comprising means for generating a first orthogonal-multi-carrier signal through N-point inverse discrete Fourier transform, the first orthogonal-multi-carrier signal having xe2x80x9cNxe2x80x9d or less orthogonal multiple carriers, where xe2x80x9cNxe2x80x9d denotes a predetermined natural number equal to or greater than 2; and means for repeating every 1-unit time segment of the first orthogonal-multi-carrier signal xe2x80x9cMxe2x80x9d times to generate every 1-symbol time segment of a second orthogonal-multi-carrier signal, the second orthogonal-multi-carrier signal having a thinned set of xe2x80x9cNxe2x80x9d or less orthogonal multiple carriers spaced at M-carrier intervals, where xe2x80x9cMxe2x80x9d denotes a predetermined natural number equal to or greater than 2.
A seventh aspect of this invention provides an apparatus comprising means for dividing every 1-symbol time segment of a first orthogonal-multi-carrier signal into xe2x80x9cMxe2x80x9d successive 1/M-symbol time segments, the first orthogonal-multi-carrier signal having a thinned set of xe2x80x9cNxe2x80x9d or less orthogonal multiple carriers spaced at M-carrier intervals, where xe2x80x9cMxe2x80x9d denotes a predetermined natural number equal to or greater than 2, and xe2x80x9cNxe2x80x9d denotes a predetermined natural number equal to or greater than 2; means for adding and averaging at least two of the xe2x80x9cMxe2x80x9d successive 1/M-symbol time segments of the first orthogonal-multi-carrier signal into a 1-unit time segment of a second orthogonal-multi-carrier signal; and means for subjecting the second orthogonal-multi-carrier signal to N-point discrete Fourier transform for every unit time interval.
An eighth aspect of this invention provides an apparatus comprising means for generating a first orthogonal-multi-carrier signal through N-point inverse discrete Fourier transform, the first orthogonal-multi-carrier signal having xe2x80x9cNxe2x80x9d or less orthogonal multiple carriers, where xe2x80x9cNxe2x80x9d denotes a predetermined natural number equal to or greater than 2; means for repeating every 1-unit time segment of the first orthogonal-multi-carrier signal xe2x80x9cMxe2x80x9d times to generate every 1-symbol time segment of a second orthogonal-multi-carrier signal, the second orthogonal-multi-carrier signal having a thinned set of xe2x80x9cNxe2x80x9d or less orthogonal multiple carriers spaced at M-carrier intervals, where xe2x80x9cMxe2x80x9d denotes a predetermined natural number equal to or greater than 2; means for generating a third orthogonal-multi-carrier signal through Mxc3x97N-point inverse discrete Fourier transform, the third orthogonal-multi-carrier signal having xe2x80x9cMxc3x97Nxe2x88x92Lxe2x80x9d orthogonal multiple carriers, where xe2x80x9cLxe2x80x9d denotes a predetermined natural number equal to or greater than the number xe2x80x9cNxe2x80x9d; and means for combining the second orthogonal-multi-carrier signal and the third orthogonal-multi-carrier signal into a fourth orthogonal-multi-carrier signal.
A ninth aspect of this invention is based on the eighth aspect thereof, and provides an apparatus further comprising means for dividing every 1-symbol time segment of the fourth orthogonal-multi-carrier signal into xe2x80x9cMxe2x80x9d successive 1/M-symbol time segments; means for adding and averaging at least two of the xe2x80x9cMxe2x80x9d successive 1/M-symbol time segments of the fourth orthogonal-multi-carrier signal into a 1-unit time segment of a fifth orthogonal-multi-carrier signal; and means for subjecting the fifth orthogonal-multi-carrier signal to N-point discrete Fourier transform for every unit time interval.
A tenth aspect of this invention is based on the eighth aspect thereof, and provides an apparatus wherein the third orthogonal-multi-carrier signal contains a pilot signal.